Add empty tuple type by lefb766 · Pull Request #14646 · microsoft/TypeScript

Nobuhiro Nakamura (lefb766) · 2017-03-14T09:09:42Z

Open question: should a non-empty tuple be assignable to []?

People may think it should be, given that you can assign [number, string] to [number].
However, the index signature of [] which is never blocks such assignment.

I think this isn't going to be a problem at least for now before variadic tuples (#5453) lands.
If you need common type of all tuples, you can simply use {}[] or any[].

Is there any other problemic scenario?

Related discussion: #6229

Nathan Shively-Sanders (sandersn) · 2017-03-16T21:41:45Z

+ return !!getPropertyOfType(type, "0") || isEmptyTupleType(type);
+ }
+
+ function isEmptyTupleType(type: Type): boolean {


you should be to use === directly, so I think you should drop isEmptyTupleType and just add || type === emptyTupleType on line 8914

Nathan Shively-Sanders (sandersn) · 2017-03-16T21:43:18Z

 // Grammar checking
- const hasErrorFromDisallowedTrailingComma = checkGrammarForDisallowedTrailingComma(node.elementTypes);
- if (!hasErrorFromDisallowedTrailingComma && node.elementTypes.length === 0) {
- grammarErrorOnNode(node, Diagnostics.A_tuple_type_element_list_cannot_be_empty);


You can delete this error from diagnosticsMessages.json since this is the only usage.

Nathan Shively-Sanders (sandersn) · 2017-03-16T21:48:53Z

+var et0 = et[0]; // never
+var et0: never;
+
+et = []; // Ok


can you add this same check in a new file, something like tupleTypesStrictNullCheck.ts, with the first line // @strictNullChecks: true to turn on strict null checks?

Nobuhiro Nakamura (lefb766) · 2017-03-20T05:14:39Z

Nathan Shively-Sanders (@sandersn) Your comments are already reflected

Marin Marinov (gcnew) · 2017-03-20T08:57:00Z

- if (elementTypes.length) {
- return createTupleType(elementTypes);
- }
+ return createTupleType(elementTypes);


I think you should update the createTupleType function to return the emptyTupleType singleton if elementTypes is empty.

Agreed. We need to make the condition persistent over future updates. A fix is pushed!

Nathan Shively-Sanders (sandersn)

Looks good to me. Ryan Cavanaugh (@RyanCavanaugh) or Anders Hejlsberg (@ahejlsberg) can you take a look too?

Mohamed Hegazy (mhegazy) · 2017-05-23T21:51:22Z


- function createTupleType(elementTypes: Type[]) {
+ function createTupleType(elementTypes: Type[]): TypeReference {
+ // We have to ensure that we get same instance for empty tuple type,


getTupleTypeOfArity caches the resulting tuple type, so not sure why we need special handling here.

Mohamed Hegazy (mhegazy)

usage of getTupleTypeOfArity should be sufficient

kiara (KiaraGrouwstra) · 2017-08-24T12:06:32Z

I've made an attempt to revive this PR taking into account the requested changes at #17762.

Nobuhiro Nakamura (lefb766) · 2017-08-24T14:20:33Z

@tycho01 oh, great! but my bad! I left this PR untouched for so long time and was even unnoticed the update on the original issue until today.

I appreciate you reused my code! Thanks!

Just wondering. Are you going to update them further and implement the additional restrictions you mentioned in #13126 (comment) ?
Currently, I'm getting difficulties finding functional update in your PR... looks they are just pure code cleaning and conflict resolution.

kiara (KiaraGrouwstra) · 2017-08-24T15:44:53Z

Nobuhiro Nakamura (@lefb766): right, I hadn't included those in there.

To answer by sub-topic there:

known length, fixing Proposal: strict and open-length tuple types #6229: I filed a separate PR for this at Make tuples have known length #17765. The reason I separated them was that adding empty tuples should be uncontroversial (explicitly marked as 'Accepting PRs' at Empty tuple type now meaningful (at least, in unions) #13126), so I didn't wanna lump them with another feature the TS team had so far been silent on.
ditch mutating methods: this was part of my original plan for that Make tuples have known length #17765, making a new Tuple interface extending ReadonlyArray with a length property. This caused the project to not compile anymore though, at which point I'd just quickly settled on letting it extend Array instead, as the length was my primary concern. I then got issues about it not seeing my new interface on half of the tests (wth), at which point I opted to just set that length directly from createTupleTypeForArity instead, foregoing the new interface as length had become its sole added feature.
no index signature: I wasn't initially convinced of this, largely in fear of breaking more still than at my ReadonlyArray attempt, though I've recently been swayed this change seems a good thing. I guess it means copying ReadonlyArray into a new Tuple interface, similar minus the index. I wish I understood why we have several copies of this interface in lib.d.ts instead of just having them extend one -- if extending is okay, I'd imagine ReadonlyArray could just be extending this Tuple interface to just add its index too.

Nobuhiro Nakamura (lefb766) · 2017-08-25T13:56:06Z

@tycho01 Thanks for explaining. I see, you have another PR.

It turns out it will be harder to find difference between #17762 and this one if I happen to solve the conflict.
I don't have idea on how to deal with this type of situation. You have?

Your investigation on the sup-topic looks interesting though. Nice work.
I have a few opinion on the topics but it may be irrelevant to write them here.

kiara (KiaraGrouwstra) · 2017-08-25T15:12:18Z

Nobuhiro Nakamura (@lefb766): wanna just stick with your PR then? If you follow mhegazy's change you may be done. :)

I'd be interested in your take on the topic, but I think the others in #13126 would be too!

Nobuhiro Nakamura (lefb766) · 2017-08-26T02:38:13Z

@tycho01 Fair point. I'll continue this work. Sorry for bothering you and others.

Nobuhiro Nakamura (lefb766) · 2017-08-27T11:39:43Z

Should be ready for review now. Mohamed Hegazy (@mhegazy) can you take a look?

I've selectively adopted @tycho01 's work.

Note: #6524 can also be closed after merge this PR.

kiara (KiaraGrouwstra) · 2018-02-14T21:57:37Z

Mohamed Hegazy (@mhegazy): conflict aside, is there more that could be done to improve this PR?

TypeScript Bot (typescript-bot) · 2018-06-18T18:35:19Z

Thanks for your contribution. This PR has not been updated in a while and cannot be automatically merged at the time being. For housekeeping purposes we are closing stale PRs. If you'd still like to continue working on this PR, please leave a message and one of the maintainers can reopen it.

Microsoft Contribution License Agreements (msftclas) added cla-required and removed cla-required labels Mar 14, 2017

Nobuhiro Nakamura (lefb766)force-pushed the empty-tuple branch from f0385d3 to 0e7ffdaCompare March 14, 2017 09:25

Nathan Shively-Sanders (sandersn) reviewed Mar 16, 2017
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Nathan Shively-Sanders (sandersn) requested changes Mar 16, 2017
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Nobuhiro Nakamura (lefb766)force-pushed the empty-tuple branch from 0e7ffda to 61ac5beCompare March 17, 2017 04:08

Marin Marinov (gcnew) reviewed Mar 20, 2017
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Nathan Shively-Sanders (sandersn) approved these changes Apr 5, 2017
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Mohamed Hegazy (mhegazy) reviewed May 23, 2017
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Mohamed Hegazy (mhegazy) suggested changes May 23, 2017
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Nobuhiro Nakamura (lefb766)force-pushed the empty-tuple branch from e02dcf3 to 1476eb4Compare July 7, 2017 16:45

ditch empty tuple check
665f44f

kiara (KiaraGrouwstra) mentioned this pull request Aug 13, 2017
allow empty tuple, fixes #13126 #17762
Closed

empty tuple tests all good
03bf0b8

Nobuhiro Nakamura (lefb766) added 2 commits August 27, 2017 15:41

Add empty tuple type
bf14cfa

Merge branch 'tycho01:13126-empty-tuple' into empty-tuple
5cffdb2

Nobuhiro Nakamura (lefb766)force-pushed the empty-tuple branch from 1476eb4 to 5cffdb2Compare August 27, 2017 08:48

Microsoft GitHub User (msftgits) removed the cla-signed label Sep 26, 2017

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kiara (KiaraGrouwstra) mentioned this pull request Jun 12, 2018
Tuples in rest parameters and spread expressions #24897
Merged

TypeScript Bot (typescript-bot) closed this Jun 18, 2018

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Open question: should a non-empty tuple be assignable to []?

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Nobuhiro Nakamura (lefb766) commented Mar 14, 2017•
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